Why does a block of iron sink but not an iron boat?

A block of iron sinks because its density is greater than that of water, meaning it displaces less water than its own weight. In contrast, an iron boat floats because its overall design includes a hollow structure that increases its volume and reduces the average density of the entire object, allowing it to displace enough water to counterbalance its weight. This principle is rooted in Archimedes' principle of buoyancy.